Wind turbine rotor blade

ABSTRACT

Wind turbine rotor blade with a blade tip, a blade root, a leading edge, a trailing edge, a pressure side, a suction side and a cross-section, which changes from the blade tip to the blade root, the longitudinal portion being arranged between the blade root and the middle of the rotor blade, has the following:
         a convex pressure side portion, which extends from the leading edge up to a pressure-side inflection point,   a concave pressure side addition portion, which connects with the pressure-side inflection point with a continuous curvature and extends up to the trailing edge,   a convex suction side portion, which extends from the leading edge up to a suction-side kink or inflection point, and   a suction side addition portion, which extends from the suction side kink or inflection point up to the trailing edge.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

BACKGROUND OF THE INVENTION

The invention relates to a wind turbine rotor blade comprising a bladetip, a blade root, a leading edge, a trailing edge, a pressure side, asuction side and a cross-section, which changes from the blade tip tothe blade root, wherein the cross-section is formed by an aerodynamicprofile in the middle of the rotor blade and is mainly circular at theblade root. Such rotor blades are used in particular for wind turbinesystems with a two- or three-blade rotor with a horizontal axis. Theyare connected at their blade root to a hub of the rotor. An assemblyflange can be designed at the blade root of the rotor blade and thepitch angle of the blade can be designed to be adjustable with the helpof a pitch drive.

Known rotor blades represent a compromise between the optimalaerodynamic shape, the requirements of the strength design and theattempt to create an economical manufacturing technique. In particular,the relative thickness of the used aerodynamic profiles must be selectedbased on strength considerations. A relatively small blade thickness ofless than 30% of the profile depth, frequently between 18% and 15% ofthe same, can be used in the aerodynamically particularly importantouter area of the rotor blades. The inner area of the rotor blades,which lies closer to the hub, plays a less decisive roll aerodynamicallyso that more deviation from the aerodynamic optimum and a relativelylarge blade thickness can be accepted in order to achieve sufficientrigidity. The aerodynamic profile then merges into the mainly circularcross-section towards the blade root. In order to improve theaerodynamic performance of the rotor blades on the inside, differentapproaches are known from the state of the art.

The use of a fin-like attachment extending longitudinally along thetrailing edge of the rotor blade is known from document WO 02/08600 A1,the entire contents of which is incorporated herein by reference. Theattachment is primarily located in a cylindrical connection area of therotor blade, which connects a rotor blade portion arranged further onthe outside and provided with an aerodynamic profile with the hub. Inthis manner, the otherwise aerodynamically ineffective connection areaalso contributes to the performance of the rotor.

A rotor blade for a wind turbine with an attached device on the pressureside near the blade root is known from document DE 10 2006 017 897 B4,the entire contents of which is incorporated herein by reference. Theknown attached device extends mainly in the longitudinal direction ofthe rotor blade. A so-called attached-device flow surface of the knownattached device begins on the pressure side at a point of the profilewhere a tangent applied to the profile runs at an angle ranging from−20° to +20° to the designed direction of flow. The attached-device flowsurface runs approximately at the angle of this tangent up to a trailingedge of the attached device that is different from the rotor bladetrailing edge, to which a rear surface of the attached device connects,which leads back to the pressure side of the profile. Comparableattached devices are also known from documents EP 2 138 714 A1, theentire contents of which is incorporated herein by reference and EP 2141 358 A1, the entire contents of which is incorporated herein byreference.

A rotor blade of a wind turbine, which is specially designed for agearless wind turbine, is known from document WO 2004/097215 A1, theentire contents of which is incorporated herein by reference. Such windturbines have a hub with a relatively large diameter. In the case ofthis known rotor blade, the aerodynamic profile of the rotor blade iscontinued mainly up to the hub, which leads to a very large profiledepth due to the large profile thickness near the hub required forreasons of rigidity. In order to achieve this, the rear area of theprofile is formed by an attachment.

A wind turbine rotor blade is known from document EP 1 845 258 A1, theentire contents of which is incorporated herein by reference, thecross-section of which has a concave pressure side addition portion in atransition area between a circular blade root and an aerodynamicprofile. The rear end of this pressure side addition portion isconnected with the trailing edge via a straight portion, which isaligned perpendicular to the profile chord and also belongs to thepressure side. The suction side of the known rotor blade is formed by aconvex portion between the leading edge and the trailing edge, whichmerges into the straight portion at the trailing edge forming an outwardpointing kink.

BRIEF SUMMARY OF THE INVENTION

The object of the invention is to provide a wind turbine rotor blade,which can be easily produced and achieves improved performance, inparticular at an inner zone of the rotor.

The wind turbine rotor blade according to the invention has a blade tip,a blade root, a leading edge, a trailing edge, a pressure side, asuction side and a cross-section, which changes from the blade tip tothe blade root, wherein the cross-section is formed by an aerodynamicprofile in the middle of the rotor blade and is mainly circular at theblade root. In a longitudinal portion of the rotor blade, thelongitudinal portion being arranged between the blade root and themiddle of the rotor blade, it has a cross-section, which comprises:

-   -   a convex pressure side portion, which extends from the leading        edge up to a pressure-side inflection point,    -   a concave pressure side addition portion, which connects with        the pressure-side inflection point in a continuous curvature and        extends up to the trailing edge,    -   a convexly curved suction side portion, which extends from the        leading edge up to a suction-side kink or inflection point, and    -   a suction side addition portion, which extends from the suction        side kink or inflection point up to the trailing edge.

Like all wind turbine rotor blades, the rotor blade according to theinvention is designed such that optimal power consumption from the windis enabled in the case of a certain relation between the rotationalspeed at the blade tip and the wind speed, i.e. in the case of theso-called design tip speed ratio, and a specified pitch angle. When therotor blade is operated at the design tip speed ratio, the air flows ina defined direction of flow at each longitudinal position of the rotorblade. This flow direction is in the following called the designeddirection of flow. The trailing edge of the rotor blade is the edge ofthe rotor blade located furthest back in the designed direction of flow.As a rule, on the trailing edge, the suction and pressure sides convergein an acute angle. In the case of rotor blades with a so-called “thicktrailing edge,” a linear portion, which is mainly arranged perpendicularto the designed direction of flow and forms a rear surface of the rotorblade, is located at the back of the profile. By definition in thiscase, the trailing edge of the rotor blade is formed by the centerpoints of the linear portions forming the “thick trailing edge.” Theleading edge of the rotor blade is the leading edge of the rotor bladefurthest apart from the trailing edge. To be distinguished from theleading edge is that point in the front area of the rotor blade at whichthe inflowing air is separated into one air current flowing along thepressure side and one flowing along the suction side. This is thestagnation point. In contrast to the position of the leading edge, thelocation of the stagnation point depends on the operating conditions ofthe rotor blade, in particular on the pitch angle. The blade root ismainly circular and can be provided with an assembly flange forfastening on a rotor hub. The pressure side is the surface locatedbetween the leading and trailing edge of the rotor blade, on whichexcess pressure is created during operation as a rule. Accordingly, thesuction side is the surface of the rotor blade between the leading edgeand trailing edge, on which negative pressure is created duringoperation as a rule. The longitudinal axis of the rotor blade is definedas a straight line through the center point of the circularcross-section at the blade root, which is aligned perpendicular to thiscircular cross-section.

The aerodynamic profile in the middle of the rotor blade is generallyequal to a wing profile of an airplane. As a rule, it has a convexsuction side, a front, convex pressure side portion and a rear, alsoconvex or concave, pressure side portion. As a rule, the two namedpressure side portions merge with a continuous curvature, i.e. without akink, where the direction of a tangent changes discontinuously.

In a longitudinal portion of the rotor blade between the blade root andthe middle of the rotor blade, the rotor blade has a cross-sectiondeviating from a conventional aerodynamic profile. This is clarified bythe terms “pressure side addition portion” and “suction side additionportion.” In other words, these portions represent extensions of thepressure or respectively suction side of a conventional profile. Besidesthis, the named terms as such are given no restricting meaning.

The aerodynamic performance in the area of the longitudinal portion isin particular improved by the convex pressure side addition portion,which amplifies the excess pressure building on the pressure side in therear area of the cross-section. This effect is technically known as“rear loading.” The concave pressure side addition portion connects witha continuous curvature to the convex pressure side portion so that thereare no flow separations in the connection area.

In contrast to the pressure side addition portion, the suction sideaddition portion does not necessarily merge with a continuous curvatureinto the suction side portion located in front, which is convexlycurved. Rather, a kink or inflection point is located between theconvexly curved suction side portion and the suction side additionportion. If one follows the progression of the convexly curved suctionside portion from the leading edge up to this kink or inflection point,there is always an inward pointing curvature, i.e. a curvature appliedto the curve is always located on the side of the suction side portionpointing towards the inside of the profile. At the kink or inflectionpoint, this curvature changes its leading sign in the case of aninflection point and first runs in the opposite direction to theoutside. In the case of a kink point, the direction of a tangent appliedto the curve also changes, namely discontinuously, wherein the curvekinks outward at the kink point. The edge formed by the kink points ofsuccessive cross-sections points inward. In both cases, the direction ofthe curve at the kink or inflection point changes with respect to thecross-section towards the outside.

The kink or inflection point can be located at approximately the samedistance from the leading edge as the pressure side inflection point. Ithas been shown that even a kink point in the cross-section of theaerodynamic performance of the profile is not detrimental, which is dueto the fact that in the case of relative profile thicknesses on theorder of magnitude considered here there are flow separations on thesuction side as a rule even in the case of a continuously curvingsurface progression. In some cases, these can also occur in thecross-section designed according to the invention. However, aparticularly material-saving construction of the rotor blade can beachieved through the kink or inflection point on the suction side of theprofile.

In one embodiment, the distance between the pressure side inflectionpoint and the leading edge, measured along the profile chord, is morethan 60% of the profile depth. The transition from the convex pressureside portion to the concave pressure side addition portion is thuslocated relatively far to the back, clearly behind the location of themaximum thickness of the profile. It was shown that the transition canalso take place at an even greater distance from the leading edge of forexample 65%, 70% or even 80% of the profile depth, without there beingflow separations. The named distances from the leading edge referrespectively to a measurement along the profile chord, i.e. to theprojection of the spatial distance in this direction. The profile chordis a straight line connecting the leading and trailing edges of theprofile.

In one embodiment, the suction side addition portion is mainly straight.The arrangement and shape of the concave pressure side addition portionand the arrangement of the trailing edge are significant for theaerodynamic effect of the profile. The suction-side connection of thetrailing edge to the convex suction side portion is of lessersignificance aerodynamically due to the already discussed flowseparations in this area. A straight-line shape of the suction sideaddition portion is particularly easy to produce and is alsoadvantageous for strength considerations.

In one embodiment, a tangent against the pressure side addition portionat the trailing edge will lie mainly in the direction of the rotor planeif the rotor blade has a pitch angle optimized for partial loadoperation. The rotor plane is mainly the plane covered by the rotorblade during rotation around the rotor axis. Strictly speaking, thisobservation only applies in the case of a rotor blade arrangedperpendicular to the rotor axis. In practice, the longitudinal axis ofthe rotor blade can also be tilted slightly with respect to thisvertical line towards the rotor axis so that the rotor blade does notrotate in a plane but rather on a cone. However, whenever “rotor plane”is referred to here and below, this means, the plane that includes thelongitudinal axis of the rotor blade in the current rotational positionof the rotor blade and a second direction, which is arrangedperpendicular to the longitudinal axis of the rotor blade andperpendicular to the rotor axis. The pitch angle optimized for thepartial load operation is the pitch angle, at which the rotor blade ispreferably operated in partial load operation. It leads to optimal powerconsumption from the wind, in particular at the design tip speed ratio.With increasing wind speed, the consumed power increases in partial loadoperation. When maximum power is reached, the power can no longer beincreased. If the wind speed continues to increase, a degradation of theaerodynamic efficiency thus is obtained by increasing the pitch angle. Aregulation of the power by controlling the pitch angle can be performedand the system is in so-called pitch-regulated operation or full loadoperation. The pitch angle optimized for partial load operation is aclearly defined variable, which is taken into consideration in thedesign of the rotor blade. The named alignment of the tangent towardsthe pressure side portion has the fact that the air flowing around therotor blade on the pressure side at the trailing edge mainly flows inthe direction of the rotor plane. The rotor blade thereby delivers anoptimal torque contribution in the area of the profile according to theinvention.

In one embodiment, a tangent lies against the suction side additionportion at the trailing edge mainly in the rotor plane when the rotorblade has a pitch angle optimized for partial load operation. Thisarrangement also contributes to an optimal torque because the airflowing on the suction side around the rotor blade also mainly flows inthe direction of the rotor plane. In particular in connection with astraight-line suction side addition portion, i.e. in the case of asuction side addition portion located entirely in the rotor blade planein partial load operation, this applies according to model calculationsalso considerating the flow separations because the formation of aseparation region with almost even thickness frequently occurs above thesuction side addition portion. This swirling air is separated by adividing streamline from the laminar air flow at a greater distance fromthe suction side addition portion. If the suction side addition portionand thus also the dividing streamline progress close to the rotor plane,the laminar air flow on the distant side of the dividing streamlinemainly in the direction of the rotor plane, which increases the createdtorque.

In one embodiment, an acute angle is formed between the pressure sideaddition portion and the suction side addition portion at the trailingedge. This benefits a smooth flowing of the air at the trailing edge inaccordance with the Kutta condition.

In accordance with one embodiment, the longitudinal portion begins at adistance from the blade root. For example, there can be a distance of0.5 m, 1.0 m or more between the blade root and the longitudinalportion. Within this distance area, the cross-section of the rotor bladecan be circular like at the blade root. A portion arranged near theblade root, where the profile is not yet designed as in the longitudinalportion, simplifies the transport and the assembly of the rotor blade.For example, a belt can be placed around this portion without damagingthe special profile in the longitudinal portion.

In one embodiment, the longitudinal portion extends up to a distancefrom the blade root, at which the cross-section has a relative profilethickness of 60% or less. It can also extend up to a cross-section witha relative profile thickness of 55%, 50%, 45% or 40%, so that theimproved “rear loading” is achieved in a larger longitudinal portion. Inthe area of even smaller relative profile thickness, the profileaccording to the invention is less suitable in contrast becauseaerodynamically good or better results can be achieved with aconventional profile without leading to excessive profile depths or veryhigh production effort.

In one embodiment, the longitudinal portion extends up to a distancefrom the blade root of 10% or more of the rotor blade length. Thelongitudinal portion can also extend up to a greater distance from theblade root of for example 15%, 20%, 25% or even 30% of the rotor bladelength so that the advantages of the invention can be obtained in alarger longitudinal portion.

In one embodiment, the rotor blade has a constant profile depth betweena first distance of 10% of the rotor blade length from the blade rootand a second distance of 15% of the rotor blade length from the bladeroot. The constant profile depth can in particular be a maximum profiledepth, which cannot easily be exceeded due to production and transportconditions. Through the cross-sectional geometry according to theinvention in this longitudinal area it is possible to improve theaerodynamic properties without exceeding the maximum profile depth. Atthe same time, the maximum profile depth in the named distance area isutilized optimally.

In one embodiment, the pressure side addition portion and the suctionside addition portion are formed by an attachment, which is connectedwith the remaining components of the rotor blade. The remainingcomponents of the rotor blade can in particular be the components of aconventional rotor blade, which is equipped with the attachment aftercompletion. The attachment can for example be screwed and/or glued tothe remaining components. Rotor blades of existing wind turbines canthereby easily be equipped with a longitudinal portion according to theinvention.

In one embodiment, the remaining components of the rotor blade at alongitudinal position of the rotor blade have a maximum profile depth,wherein the attachment begins at this longitudinal position and extendsfrom there in the direction of the blade root. The longitudinal areawith the maximum profile depth of a conventional rotor blade denotesthat point where the transition from an aerodynamically optimal profileto the circular cross-section at the blade root begins. The attachmentcan thus particularly advantageously start from this point.

In one embodiment, the remaining components of the rotor blade at alongitudinal position of the rotor blade have a maximum profile depth,wherein the attachment begins at a greater distance from the blade rootthan this longitudinal position and extends from there in the directionof the blade root, and the profile depth of the rotor blade is enlargedthrough the attachment at least in a longitudinal portion above andbeyond the maximum profile depth of the remaining components. Themaximum profile depth of the remaining components of the rotor blade canbe defined for example by restricting transport or productionconditions. If an attachment is added to these remaining componentsafter transport or respectively after production, the maximum profiledepth can in some cases thereby be exceeded without or with littleadditional effort. A larger profile depth can thereby be used with thehelp of the attachment in the longitudinal portion.

In one embodiment, the attachment is subdivided into several segments.It is thus easier to handle and assemble. The segments can in particularbe strung together in the longitudinal direction of the rotor blade,wherein a distance that enables a relative movement between the segmentscan be located between two segments. The distance can for example befilled with an elastic adhesive. The connection of the attachment withthe remaining components of the rotor blade is thereby less heavilystressed, in particular in the case of a deformation of these remainingcomponents when loaded.

In one embodiment, the attachment is shell-like, i.e. it is made of acurved jacket with a mainly even thickness. One side of the jacket formsthe pressure side addition portion, the opposite-lying side of thejacket the suction side addition portion. The jacket is connected withthe remaining components of the rotor blade such that the pressure sideis continued in a continuously curved manner by the pressure sideaddition portion. This embodiment is particularly easy to implement froma structural point of view.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is explained in greater detail below based on exemplaryembodiments shown in the figures.

FIG. 1 a top view of the suction side of a rotor blade according to theinvention,

FIG. 2 a top view of the suction side of a conventional rotor bladeaccording to the prior art,

FIG. 3 a perspective view of a portion of the rotor blade from FIG. 1,

FIG. 4 another perspective view of a portion of the rotor blade fromFIG. 1,

FIG. 5 a top view of the trailing edge of a portion of the rotor bladefrom FIG. 1,

FIG. 6 a top view according to FIG. 5 with additional highlighting,

FIG. 7 a top view of the pressure side of a portion of the rotor bladefrom FIG. 1,

FIG. 8 a top view of the suction side of a portion of the rotor bladefrom FIG. 1,

FIG. 9 a cross-section through the rotor blade from FIG. 1 in across-sectional plane located 2 meters from the rotor axis,

FIG. 10 a cross-section through the rotor blade from FIG. 1 in across-sectional plane located 2.5 meters from the rotor axis,

FIG. 11 a cross-section through the rotor blade from FIG. 1 in across-sectional plane located 3 meters from the rotor axis,

FIG. 12 a cross-section through the rotor blade from FIG. 1 in across-sectional plane located 3.5 meters from the rotor axis,

FIG. 13 a cross-section through the rotor blade from FIG. 1 in across-sectional plane located 4 meters from the rotor axis,

FIG. 14 a cross-section through the rotor blade from FIG. 1 in across-sectional plane located 5 meters from the rotor axis,

FIG. 15 a cross-section through the rotor blade from FIG. 1 in across-sectional plane located 6 meters from the rotor axis,

FIG. 16 a cross-section through the rotor blade from FIG. 1 in across-sectional plane located 7 meters from the rotor axis,

FIG. 17 a cross-section through the rotor blade from FIG. 1 in across-sectional plane located 8 meters from the rotor axis,

FIG. 18 a cross-section through the rotor blade from FIG. 1 in across-sectional plane located 9 meters from the rotor axis,

FIG. 19 a cross-section through the rotor blade from FIG. 1 in across-sectional plane located 10 meters from the rotor axis,

FIG. 20 the cross-sections from FIGS. 9 through 19 in a jointrepresentation,

FIG. 21 a representation of the flow lines in a cross-sectional planethrough the rotor blade in accordance with FIG. 13, and

FIG. 22 a cross-section through another exemplary embodiment of a rotorblade according to the invention with a shell-like attachment.

The same reference numerals are used for the same parts in all figures.

DETAILED DESCRIPTION OF THE INVENTION

While this invention may be embodied in many different forms, there aredescribed in detail herein a specific preferred embodiment of theinvention. This description is an exemplification of the principles ofthe invention and is not intended to limit the invention to theparticular embodiment illustrated.

In FIG. 1, the entire rotor blade is shown in a top view of the suctionside. It has a length of just under 50 meters from the blade tip 10 tothe blade root 12. At the blade root 12, the rotor blade has a circularcross-section. The blade root 12 has a circular assembly flange notshown in the figures, which is mounted to the rotor hub. The blade root12 is then located at a distance of approximately 1.5 m from the rotoraxis.

Over the bulk of its length, the rotor blade has an aerodynamic profilein cross-section, in particular in the middle 14 of the rotor blade. Theleading edge 16 of the rotor blade is located in the representation inFIG. 1 mainly on the right edge of the shown rotor blade; the trailingedge 18 is formed by the left edge of the rotor blade.

In a longitudinal portion of the rotor blade, an attachment 20 isarranged, which forms the trailing edge 18 in this longitudinal portion.The shape of the attachment 20 is described in detail below.

FIG. 2 shows a conventional rotor blade according to the prior art,which can be fitted with an attachment 20 to create a rotor bladeaccording to the invention in accordance with FIG. 1. Insofar as theinvention is achieved through the connection of the attachment 20 with aconventional rotor blade, for example in accordance with FIG. 2, theconventional rotor blade in the language usage of this application formsthe other or remaining components of the rotor blade. The attachment 20can for example be glued to and/or screwed in these other components.

A comparison of FIGS. 1 and 2 shows that the rotor blade according tothe invention with attachment 20 in accordance with FIG. 1 differs fromthe conventional rotor blade in accordance with FIG. 2 among otherthings in the progression of its profile depth. In a conventional rotorblade in accordance with FIG. 2, the profile depth first increases in amonotonic manner beginning from the blade tip 10 in the direction of theblade root 12 until a maximum profile depth is reached at thelongitudinal position designated 22. Beginning from the longitudinalposition 22, the profile depth decreases again towards the blade root12, wherein the aerodynamic profile merges into the circularcross-section, which it also has in the area of the blade root 12, at athird cross-section designated 24. The transition of the profile depthtakes place continuously along a continuously differentiable curve. Inthe invention in accordance with FIG. 1, the profile depth from theblade tip 10 to the longitudinal position 22 with maximum profile depthhas the same progression as in FIG. 2. However, from the longitudinalposition 22 to the blade root, the profile depth first remains constantin the longitudinal portion 26 in order to then decrease to the circularcross-section. The transition from the aerodynamic profile to thecircular cross-section takes place in turn at the third cross-section24, wherein the profile depth at this position changes upon formation ofa kink. The curve describing the trailing edge 18 is thus notcontinuously differentiable at this point.

The longitudinal portion 26 with a constant profile depth extendsapproximately over an area between a first distance of 10% of the rotorblade length from the blade root and a second distance of approximately20% of the rotor blade length of the blade root.

In the perspective view of FIG. 3, the shape of the attachment can beidentified more exactly. The shown portion of the rotor blade begins atthe blade root 12 and shows approximately the blade-root-side third ofthe rotor blade. Like FIGS. 4 through 8, the representation originatesfrom an aerodynamic model calculation, in which the hub of the rotor isrepresented by a sphere 28. A part of this sphere 28 is also shown inFIGS. 3 through 8, but does not belong to the rotor blade. One can seethe circular cross-section of the rotor blade in FIG. 3 in the area ofthe blade root 12 and can sense the aerodynamic profile of the rotorblade, which mainly corresponds with that of an airplane bearingsurface, on the right edge of the figure. The side of the rotor bladelocated on top in the representation is the suction side 30; thepressure side 32 is located on the bottom side and is only partiallyvisible in FIG. 3.

A part of the suction side 30 and a part of the pressure side 32 areformed by the attachment 20. For this, the attachment 20 comprises asingle convexly curved suction side addition portion 34 and a doubleconcavely curved pressure side addition portion 36. The suction sideaddition portion 34 and the pressure side addition portion 36 runtogether at the trailing edge 18 by forming an acute angle. The suctionside addition portion 34 merges into the parts of the suction side 30formed by the remaining components of the rotor blade at a curved line38. The pressure side addition portion 36 merges into the parts of thepressure side 32 formed by the remaining components of the rotor bladeat another curved line 40.

As seen from the blade root 12, the attachment 20 begins at a point 42,where the curved lines 38 and 40 as well as the trailing edge 18 runtogether. The attachment ends at another point 44 where the curved lines38 and 40 and the trailing edge 18 run together one more time. The point42 forms the blade-root-side end of the attachment 20. The point 44forms the blade-tip-side end of the attachment 20. At 46, the remainingcomponents of the rotor blade have a thick trailing edge, i.e. in thisarea the trailing edge of the remaining components of the rotor blade isformed by a surface lying mainly perpendicular to the direction of flow.However, in the area of attachment 20, this surface does not form thetrailing edge 18 of the rotor blade, which is formed by attachment 20.

Rather than with the help of an attachment 20, the rotor blade geometryaccording to the invention can already be taken into consideration inthe design of a new rotor blade. In this case, for example, the upperand lower shells respectively can be produced as one piece with asuction side addition portion 34 and a pressure side addition portion36.

FIG. 4 shows another perspective view of the rotor blade portion in FIG.3. Particularly well discernible is the blade-root-side part of thesuction side addition portion 34, which tapers off acutely in point 42,which marks the blade-root-side end of the attachment 20. Alsodiscernible is that the curved line 38, which marks the transition ofthe suction side addition portion 34 into the parts of the suction side30 formed by the remaining components of the rotor blade, is arrangedrelatively far back with respect to the profile depth. It is locatedclearly behind the location of the maximum thickness of the profile ateach longitudinal position of the rotor blade.

In the top view in FIG. 5, the trailing edge 18 of the rotor blade isvisible. If it is formed by the attachment 20, the suction side additionportion 34 leading to the trailing edge 18 runs perpendicular to thedrawing plane so that it disappears behind the trailing edge 18. Thepressure side addition portion 36 on the other hand is well visible.Also visible is the blade-root-side end of the attachment 20 at point 42and the blade-tip-side end of the attachment 20 at point 44. In therepresentation in FIG. 5, the drawing plane runs perpendicular to therotor plane, wherein a pitch angle of the rotor blade is assumedaccording to the pitch angle optimized for the partial load operation.The drawn-in angle α₁ is measured in the drawing plane, i.e. in a planearranged perpendicular to the rotor plane and parallel to thelongitudinal axis of the rotor blade. It is defined between the rotorplane, the direction of which is indicated by 48, and the tangentialplane 50. The tangential plane 50 is applied to the pressure side,namely to the trailing edge 18 at the third cross-section 24, i.e.mainly at point 42. The angle α₁ advantageously lies in a range from 30°to 90°. In the exemplary embodiment shown, it is approximately 45°.

FIG. 6 shows the same view as FIG. 5; however, the progression of thetrailing edge 18 is highlighted. In the projection on the shown drawingplane, i.e. on a plane arranged perpendicular to the rotor plane andparallel to the longitudinal axis of the rotor blade, the trailing edge18 rises starting from the blade tip 10 at first in a strictly monotonicmanner until it reaches its highes point at a second cross-section 52and then falls towards the blade root 12 down to the third cross-section24 in a strictly monotonic manner. Between the second cross-section 52and the third cross-section 24, the progress of the trailing edge 18 andthus the alignment of the profile chord do not follow the direction offlow, which turns continuously further towards the direction of therotor axis. A trailing edge following this turning direction of flowwould approximately take the progress shown by 54, as is the case forexample with the rotor blade known from the document WO 2004/097215 A1discussed above.

FIG. 7 shows another top view of the portion of the rotor bladeaccording to the invention shown in the previous figures. The drawingplane is the rotor plane, wherein again a pitch angle according to thevalue optimized for the partial load operation is assumed. The viewfocuses on the pressure side 32 of the rotor blade. Well discernible isthe longitudinal portion 26, in which the profile depth of the rotorblade is constant.

The drawn-in angle α₂ is measured in the drawing plane, i.e. in therotor plane. It is defined between the longitudinal axis of the rotorblade, which runs parallel to the line 56, and the projection of thetangent 58 on the trailing edge of the rotor blade at the thirdcross-section 24 onto the rotor plane. The angle α₂ advantageously liesin a range from 25° to 90°. In the exemplary embodiment shown, the angleα₂ is approximately 45°. In contrast to a conventional rotor blade inaccordance with FIG. 2, the trailing edge 18 flows into the cylindrical,blade-root-side portion of the rotor blade forming an angle rather thana continuously differentiable curve in the area of the thirdcross-section 24.

FIG. 8 clarifies in particular the sectional planes selected for FIGS. 9through 19 based on a top view of the suction side 32. Thecross-sections shown in these figures mainly cover the longitudinalportion of the rotor blade provided with the attachment 20 where therotor blade has a special profile. The cross-section in FIG. 9 runsalong the longitudinal position of the already explained thirdcross-section 24, i.e. on the blade-root-side end of the attachment 20.The other cross-sections in FIGS. 10 through 19 have an increasingdistance from the blade root, wherein the cross-section in FIG. 19 isarranged near the blade-tip-side end of the attachment 20, i.e. nearpoint 44. At point 44, where the attachment 20 and thus the longitudinalportion of the rotor blade with the special profile end, the relativeprofile thickness is 60% or less. Point 44 is spaced from the blade root12 at a distance of 10% or more of the rotor blade length.

The longitudinal portion of the rotor blade with the special profilebegins at the third cross-section 24 at a distance from the blade root12 of at least 0.5 meters, in the example at a distance of approximately1 meter. The curved line 38 where the suction side addition portion 34merges into the parts of the suction side 30 formed by the othercomponents of the rotor blade is also visible in FIG. 8.

The features of the special profile in the area of the namedlongitudinal portion are first explained based on FIG. 11. In thecross-section in FIG. 11, the positions are sown of the longitudinalaxis 60 of the rotor blade is approximately in the middle of the showncross-section and of the trailing edge 18. Trailing edge 18 andlongitudinal axis 60 are connected together by a straight line 62. Theleading edge 16 of the rotor blade is marked in the cross-section by across. Also drawn in is the front stagnation point 64 of the profile andthe designed direction of flow 66, which is indicated by a line pointingto the front stagnation point 64. The rotor plane 68 is also drawn in asthe reference plane. The rotor plane 68 includes the longitudinal axis60 and is aligned perpendicular to the dashed-line rotor axis 70. It isunderstood that the rotor axis 70 lies outside the shown sectionalplane.

The profile shown in FIG. 11 has a convex suction side portion 72, whichextends from the leading edge 16 up to a suction-side kink point 74. Asuction side addition portion 76 runs in a straight line from the kinkpoint 74 to the trailing edge 18. The pressure side of the profile isformed by a convex pressure side portion 78, which extends from theleading edge 16 up to a pressure-side inflection point 80, and by aconcave pressure side addition portion 82, which extends from thepressure-side inflection point 80 up to the trailing edge 18.

A tangent applied to the concave pressure side addition portion 82 inthe area of the trailing edge 18 is mainly aligned in the direction ofthe rotor plane 68. The suction side addition portion 76 also runs inthe direction of the rotor plane 68. An acute angle is formed betweenthe ends of the suction side addition portion 76 and the pressure sideaddition portion 82 adjacent to the trailing edge 18.

The angle α₃ is defined between the rotor plane 68 as reference planeand the straight line 62. The position of the trailing edge 18 in thecross-section is described by angle α₃.

The named features also exist in the remaining cross-sections in FIGS. 9through 19 and are designated with the same reference numerals. Theprofile chord 84, which runs from the leading edge 16 to the trailingedge 18, is also drawn in FIG. 12. The projection of the pressure-sideinflection point 80 on the profile chord 84 is also shown. The distance86 of the pressure-side inflection point 80 from the leading edge 16designated 86 and measured along the profile chord 84 is approximately75% of the profile depth at the longitudinal position of the rotor bladeshown in FIG. 12.

The angle α₃ assumes approximately the following values at thelongitudinal positions of the cross-sections shown in FIGS. 9 through19: FIG. 9: −22.5°, FIG. 10: −2°, FIG. 11: 8°, FIG. 12: 13°, FIG. 13:15.5°, FIG. 14: 16°, FIG. 15: 12°, FIG. 16: 7°, FIG. 17: 3.5°, FIG. 18:2°, FIG. 19: 0°. The angle α₃ thus assumes a maximum approximately atthe longitudinal position of the cross-section in FIG. 14. Thislongitudinal position corresponds with the second cross-section 52.Starting from a longitudinal position (not shown) near the blade tip,the angle α₃ increases in a strictly monotonic manner towards the bladeroot up to the longitudinal position of the second cross-section 52,reaches a maximum at the second cross-section 52 and then decreases in astrictly monotonic manner up to the third cross-section 24.

The cross-section in FIG. 19 is located at a longitudinal position ofthe rotor blade near the blade-tip-side end of the attachment 20. Inthis position, the relative profile thickness is approximately 50%.

In FIGS. 17, 18 and 19, the “thick trailing edge” of the remainingcomponents of the rotor blade is also visible and designated withreference number 46. It is to be differentiated from the trailing edge18 of the rotor blade.

In FIG. 20, the cross-sections in FIGS. 9 through 19 are shown withsuperimposed longitudinal axis 60. In this representation, thetransition from an almost circular cross-section, as shown in FIG. 9, tothe cross-section in FIG. 19, which already mainly corresponds with anairfoil-like, aerodynamic profile, is visible. Also discernible is thedesigned direction of flow 66 turning with decreasing distance from theblade root further in the direction of the rotor axis 70. This turningof the designed direction of flow 66 is shown by arrow 85. Furthermore,the curved progression of the trailing edge 18, which reaches a maximumin the cross-section in FIG. 14, can be gathered from the representationin FIG. 20.

FIG. 21 shows in a cross-sectional plane the air flow forming around therotor blade during operation. Well discernible is the front stagnationpoint 64 where the air separates into a part flowing over the suctionside and one flowing over the pressure side. The flow lies close to theprofile in the area of the pressure side. On the trailing edge 18, itflows smoothly in the direction of the rotor plane, again at the pitchangle optimized for partial load operation. Above the straight-linesuction side addition portion 76, beginning approximately from the point86 of the convex suction side portion 72, there are flow separations anda turbulent area 88 forms. The dividing streamline 90 separates theturbulent area 88 from the flow progressing again in a laminar manner ata greater distance from the suction side addition portion 76 in area 92.The divided streamline 90 progresses almost parallel to the suction sideaddition portion 76 and to the rotor plane.

FIG. 22 shows a cross-section of another exemplary embodiment of a rotorblade. The cross-section has the already explained features, which aredesignated with the same reference numerals as in the first exemplaryembodiment. The attachment 20, which has the suction side additionportion 76 and the pressure side addition portion 82, is formed by ashell-like component. The shell-like component has an even thickness sothat the suction side addition portion 76 and the pressure side additionportion 82 are located at a constant distance from each other. Thetransition from the attachment 20 to the remaining components of therotor blade runs on the pressure-side inflection point 80 with acontinuous curvature, on the suction-side kink point 74 forming aninward pointing kink.

This completes the description of the preferred and alternateembodiments of the invention. Those skilled in the art may recognizeother equivalents to the specific embodiment described herein whichequivalents are intended to be encompassed by the claims attachedhereto.

What is claimed is:
 1. A wind turbine rotor blade comprising a blade tip(10), a blade root (12), a leading edge (16), a trailing edge (18), apressure side (32), a suction side (30) and a cross-section, whichchanges from the blade tip (10) to the blade root (12), wherein thecross-section in the middle (14) of the rotor blade is formed by anaerodynamic profile and is mainly circular at the blade root (12), andwherein the cross-section in a longitudinal portion of the rotor blade,the longitudinal portion being arranged between the blade root (12) andthe middle (14) of the rotor blade, comprises: a convex pressure sideportion (78), which extends from the leading edge (16) up to apressure-side inflection point (80), a concave pressure side additionportion (82), which connects with the pressure-side inflection point(80) with a continuous curvature and extends up to the trailing edge(18), a convex suction side portion (72), which extends from the leadingedge (16) up to a suction-side kink or inflection point (74), a suctionside addition portion (76), which extends from the suction-side kink orinflection point (74) up to the trailing edge (18), and wherein the kinkor inflection point (74) is formed such that if one follows aprogression of a curve defined by the convex suction side portion (72)and the suction side addition portion (76) from the leading edge (16) upto the kink or inflection point (74), a direction of the curve changesat the kink or inflection point (74) towards an outside of thecross-section.
 2. The wind turbine rotor blade according to claim 1,wherein a distance from the pressure-side inflection point (80) to theleading edge (16), measured along the profile chord (84), is more than60% of a profile depth.
 3. The wind turbine rotor blade according toclaim 1, wherein the suction side addition portion (76) is mainlystraight.
 4. The wind turbine rotor blade according to claim 1, whereina tangent lies against the pressure side addition portion (82) at thetrailing edge (18) mainly in a rotor plane when the rotor blade isarranged with reference to the rotor plane at a pitch angle optimizedfor partial load operation.
 5. The wind turbine rotor blade according toclaim 1, wherein a tangent lies against the suction side additionportion (76) at the trailing edge (18) mainly in a rotor plane when therotor blade is arranged with reference to the rotor plane at a pitchangle optimized for partial load operation.
 6. The wind turbine rotorblade according to claim 1, wherein an acute angle is formed between thepressure side addition portion (82) and the suction side additionportion (76) at the trailing edge (18).
 7. The wind turbine rotor bladeaccording to claim 1, wherein the longitudinal portion begins at adistance from the blade root (12).
 8. The wind turbine rotor bladeaccording to claim 1, wherein the longitudinal portion extends up to adistance from the blade root (12), in which the cross-section has arelative profile thickness of 60% or less.
 9. The wind turbine rotorblade according to claim 1, wherein the longitudinal portion extends upto a distance of 10% or more of a rotor blade length from the blade root(12).
 10. The wind turbine rotor blade according to claim 1, wherein therotor blade has a constant profile depth between a first distance of 10%of a rotor blade length from the blade root (12) and a second distanceof 15% of the rotor blade length from the blade root (12).
 11. The windturbine rotor blade according to claim 1, wherein the pressure sideaddition portion (82) and the suction side addition portion (76) areformed by an attachment (20), which is connected with the remainingcomponents of the rotor blade.
 12. The wind turbine rotor bladeaccording to claim 11, wherein remaining components of the rotor bladeat a longitudinal position (22) of the rotor blade have a maximumprofile depth, wherein the attachment (20) begins at this longitudinalposition (22) and extends from there in the direction towards the bladeroot (12).
 13. The wind turbine rotor blade according to claim 11,wherein remaining components of the rotor blade at a longitudinalposition (22) of the rotor blade have a maximum profile depth, whereinthe attachment (20) begins at a greater distance from the blade root(12) than this longitudinal position (22) and extends from there in thedirection towards the blade root (12) and the profile depth of the rotorblade is enlarged by the attachment (20) above and beyond the maximumprofile depth of the remaining components at least in a longitudinalportion.
 14. The wind turbine rotor blade according to claim 11, whereinthe attachment (20) is subdivided into several segments.
 15. The windturbine rotor blade according to claim 11, wherein the attachment (20)is formed by a shell-like component made of a curved jacket with eventhickness.